Definition: You are given a question on human sexuality. You are also given 4 answer options (associated with "A", "B", "C", "D"), out of which only one is correct. You need to answer the question by selecting the correct option. You should only answer with the choice letter, not the whole answer.
Input: Menstrual cramps may be caused, in part, by:
(A)low levels of prostaglandin (B)an increased oxygen supply to the uterus (C)highly sensitive nerve endings (D)frequent masturbation

A